This invention relates generally to a press system or the like and more specifically to a press system having improved valve assembly for controlling the fluid pressure in a cylinder chamber. The valve assembly may advantageously be utilized in systems other than a press system.
The metal stamping industry has utilized press systems similar to those disclosed in U.S. Pat. Nos. 3,202,411 and 3,636,749 to Heiser to form products of many different configurations. These presses have included a pressure pad which is supported by a die cylinder. During operation of the press, a ram is moved downwardly and the pressure pad is driven against the die cylinder. When a predetermined fluid pressure has been obtained in a die cylinder chamber, a pressure relief valve is actuated to relieve the hydraulic fluid pressure. Most of the pressure relief valves in general use depend upon the movement of mechanical parts to effect their operation between a closed position and an open position in which the fluid pressure is exhausted from the die cylinder chamber.
It is believed that the mechanical parts of these relief valves just do not move as fast as demanded by the operating characteristics of the press system. It is believed that this lack of response is due to the inertia of the various parts of the relief valve assembly. Thus, upon closing of the press there is an instantaneous surge of hydraulic fluid pressure in the die cylinder chamber. The surge results in a pressure shock peak occurs before the movable parts in a mechanical relief valve assembly can be actuated to relieve the peak pressure. Similarly, an immediate response is necessary to compensate for a rapidly diminishing or fading flow which may occur after the initial pressure surge.
In a prior art press system, the flow of hydraulic fluid from the cylinder chamber and the maintenance of the desired system pressure is dependent upon mechanical movement of a valve element. This valve element must effects a precise variation in an orifice to maintain the desired pressure in the die cylinder. Due to manufacturing tolerances, wear of mechanical parts and inertia effects, the mechanical valve member may not vary the orifice size in the precise manner required for optimum press operation. For these and other reasons, the pressure requirements for a given die may never be obtained during operation of the prior art press system. This has resulted in an experimental procedure in setting up and operating of the prior art press system.